Quality control systems for detecting leaks of gaseous or liquid materials from closed containers

ABSTRACT

A system for testing systems which are in turn used to test the leaktightness of a hollow body is suggested. Instead of the hollow body, a test body ( 2 ) is placed in the system which generates a defined pressure increase in a measuring chamber ( 4 ) within a pre-determined time span. This defined pressure increase corresponds exactly to the pressure increase generated by a hollow body with a small amount of leakage, wherein the hollow body can still just be regarded as leaktight. The test body can be configured as a glass capillary which extends in a sealing manner between two chambers with different air pressure. Alternatively, the test body can comprise a material which can accept a defined amount of moisture from the ambient atmosphere during storage. A vacuum formed around the test body causes moisture to be withdrawn from the test body and at least partially evaporated in the vacuum, which again leads to an increase in pressure in the chamber. This pressure increase again corresponds to the just-tolerable pressure increase of a hollow body which is to be tested.

This application is a continuation-in-part of prior provisionalapplication U.S. Ser. No. 60/291,876, which was filed on May 18, 2001,and claims priority under 35 U.S.C. §119 therefrom.

BACKGROUND OF THE INVENTION

Plants and systems for testing whether a hollow body encasing gases orliquids (usually under pressure) is leaktight often operate according tothe pressure maintaining principle. Here, the hollow body which is to betested is surrounded with a vacuum. If the vacuum remains constant overthe test period, the hollow body is considered leaktight. However, ifthe vacuum decreases and the pressure increases beyond a pre-determinedfixed value, the hollow body is considered to be leaky.

Containers or cartridges for medical fluids or dosing aerosols forinhalers are named as examples of test subjects from the field ofmedicine. For example, reference is made to documents EP 0 775 076 B1,WO 00/49988, WO 97/39831 and WP 00/23037. All of the cartridges orcontainers described therein must be tested for their leaktightness. Themethods used to this end include systems employing thehereinbefore-mentioned pressure-maintaining principle. The disclosuresof such publications are herein incorporated by reference.

In order to guarantee the continuity of the test process, it isnecessary to test the system itself via which the leaktightness of thehollow body is checked. An examination is carried out as to whether themeasured pressure increase due to leakage is accurately measured andwhether the correct conclusions are drawn from the measured values. Itis therefore necessary to subject the leaktightness testing systemitself to an examination from time to time.

In accordance with this, it is the object of the present invention tospecify an examination system for such a leaktightness testing system.

THE INVENTION

In systems for testing hollow bodies, e.g., medical cannisters, todetermine whether such cannisters or bodies are leaky, the cannister orhollow body (filled with gas or liquid) is placed in a vacuum. If thevacuum remains constant over a specified test period, then the cannisteror hollow body is deemed leak-tight. However, if the vacuum decreasesand the pressure increases beyond a pre-determined value, then thehollow body or cannister can be considered to be leaky. These systemsmust also undergo integrity checks. Accordingly, the present inventorhas determined that the integrity of such systems can be ascertained byusing, in place of the hollow body or cannister, a test body havingcertain characteristics. These characteristics allow reliable statementsto be made as to whether the leaktightness testing system is functioningcorrectly.

This object is solved by the system according to the present invention,making reference to the drawings appended hereto.

Consequently, according to the first solution suggestion, a system fortesting systems which in turn are used to check that a hollow body isleaktight is suggested wherein instead of the actual hollow body whichis to be tested for leaktightness, a test body is placed in a testchamber which is separated into two chambers in such a way that oneportion of the test body is exposed to the first chamber, which is atambient pressure, and another portion of the test body is exposed to thesecond chamber which is at reduced air pressure. Here, the two chambersare separated from one another by means of a seal. The test body extendsin a sealing manner through a penetration in the seal. Hence it isensured that both chambers are separated from one another with regard topressure. The test body has a defined leakage with a pre-specifiedleakage rate which corresponds to the amount of leakage which is stilljust acceptable in order for the hollow body to be defined as leaktight.As a result of the defined leakage, there is now a pressure increase inthe second chamber which has lower air pressure. This pressure increaseis measured over a certain period of time. If the measured leakage rateexceeds the pre-specified maximum leakage rate, it can be concluded thatthe entire system is not functioning correctly, since an additional leakmust have appeared in the system or the measuring apparatus must not befunctioning correctly. The operating personnel of the leaktightnesstesting system can then implement suitable measures to return theleaktightness testing system to its proper working condition.

A test body according to the invention for use in thehereinbefore-described system is configured so that the pre-specifiedleakage is realized by a glass capillary of given length and givendiameter. This glass capillary therefore penetrates thehereinbefore-described seal between the two chambers of the test chamberwhich have different air pressures. Correspondingly, the glass capillarysimulates a hollow body, for example a cartridge according to the abovedocuments, with maximum tolerable leakage. Here, in a specialapplication case the leakage rate of the glass capillary is 6.67×10⁻³mbar/sec x₁ for ambient atmosphere (ambient air).

This value corresponds to the maximum tolerable value for the cartridgesor hollow bodies.

For reasons of practicality, the glass capillary is preferably supportedby a sealed hollow body.

The given leakage of the glass fibres is preferably pre-specified by thediameter of the capillary, which, for this example, lies in the range ofmax. 50 μm.

According to the second embodiment of the present invention, a system isprovided for the testing of systems which in turn are used to check thata hollow body is leaktight wherein instead of the hollow body, a testbody is placed in a vacuum chamber, wherein a defined amount ofmoistness is supplied to the test body in advance and an increase inpressure is measured in the vacuum chamber within a predetermined timespan. If this measured pressure increase exceeds a given maximumpressure increase, it can be assumed that the leaktightness testingsystem is faulty.

The basis for this system is that the test body comprises a materialwhich can absorb a defined amount of moistness from the ambientatmosphere during storage. The quantity of absorbable moistness can,among other things, be influenced by the size of the surface of the testbody.

A vacuum is now generated around the test body in the vacuum chamber.During the test period, moisture is removed from the test body and isevaporated at least in part in the vacuum. This evaporation increasesthe pressure in the vacuum chamber. Dependent on the time span and thequantity of absorbed moisture, a defined pressure rise in the vacuumchamber is produced. This correlates with a just-tolerable pressure risein the hollow body which is to be tested for leaktightness, the actualtest subject of the leaktightness testing system.

Common to both systems is that the actual leaktightness testing systemis calibrated in that the just-tolerable leakages are simulated, and inthe actual test process. Exceeding those pre-determined parameters is aclear indication of additional leakages or other failures in the systemfunction.

As already mentioned, in the case of the system according to the secondembodiment, the test body comprises a special material. Materials to beused are those which have a relatively high absorbency capacity formoisture. The use of polyamide or polyoxymethyl is preferred.

A great advantage of all suggested test bodies is that these can bere-used after a recovery time. In the case of the system according tothe first solution suggestion, pressure equilibration with thesurroundings takes place during the recovery time after the test. In thecase of the system according to the second solution suggestion, renewedabsorption of moisture from the surroundings, with climate beingconstant, takes place after the test.

The invention is described with reference to two examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically, the system according to the first embodiment,

FIG. 2 the system according to the first embodiment, ready to use,

FIG. 3 the system of FIG. 2 during the test, and

FIG. 4 the system according to the second embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following text, the same reference numerals designate identicalparts.

FIG. 1 schematically shows the first system. It substantially comprisesthe test chamber 5 in which the actual test subject, namely the hollowbody, is placed after the leaktightness testing system has beenrecognized as ready to use. However, in order to test this system, thetest body 2 is used. The test body 2 extends through a seal 6 via whichthe lower part of the test chamber 5 is sealed, separating off a firsttest chamber 3 which is generally at ambient pressure.

In the present case, the test body 2 comprises a hollow body and adefined leak which is realized by a glass capillary 7 of given lengthand given diameter. In order to implement the test, a suction vessel 8is placed on the seal 6 and the thus-defined space is evacuated untilthe pressure therein is approximately 1 mbar. The suction vessel 8encloses the second chamber 4 of the test chamber 5. If the air pressurein the first chamber 3 is approximately 1000 mbar and is approximately 1mbar in the second chamber 4, the pressure difference between the twochambers is 999 mbar. Together with the glass capillary 7 of the testbody 2, a certain pressure equilibration takes place between thechambers 3 and 4 within a given period of time. This is shownschematically in FIG. 3, where the air stream through the glasscapillary 7 is indicated by the arrow 9.

The dimensions of the glass capillary 7 are selected so that the leakagerate corresponds to leakage rate which indicates that the leakage isjust acceptable in the case of the hollow body which is to be tested.

The leakage rate is determined by seniors (not illustrated). If theleakage rate exceeds a given value, it can be inferred that the systemas such does not comply with the requirements for further use in theleaktightness testing process. Additional leakage is then the main causeof faulty function.

FIG. 4 schematically shows the second suggested system. A test body 20is placed in a vacuum chamber 20. A vacuum is generated around this testbody in the vacuum chamber 30. Following this, moisture is withdrawnfrom the test body 20 during the test phase and is at least partiallyevaporated in the vacuum. This evaporation increases the pressure in thevacuum chamber 30, which can be measured by sensors (not illustrated).This rise in pressure corresponds to that which is just tolerable in thecase of hollow bodies which are to be tested in the leaktightnesstesting system for their leaktightness.

What is claimed is:
 1. A method for testing systems which are used todetermine whether any given hollow body is leaktight wherein a test body(2) is placed in a test chamber (5) which is separated into two chambers(3,4) in such a way that one portion of the test body (2) is exposed tothe first chamber (3), which is at ambient pressure, and another portionof the test body is exposed to the second chamber (4), which is atreduced air pressure, wherein both chambers (3,4) are separated from oneanother by means of a seal (6) and the test body (2) extends in asealing manner through a penetration in the seal, and the test body (2)has a defined leakage with a pre-specified leakage rate, which comprisesmeasuring the pressure increase in the second chamber (4) over a periodof time, and calculating if the measured leakage rate exceeds thepre-specified leakage rate, so that it can be determined whether theleaktightness testing system is functioning correctly.
 2. The method asrecited in claim 1, wherein the pre-determined leakage rate in the testbody is realized by a glass capillary (7) of pre-determined length andpre-specified diameter.
 3. The method as recited in claim 2, wherein theglass capillary (7) has a diameter no greater than about 50 μm.